1. Field of the Invention
The field of the invention is that of cellular mobile radio systems. To be more precise, the invention concerns the spatial location of a mobile station in a cell of a communication network with relatively good accuracy and in particular with sufficient accuracy for space division multiple access (SDMA) systems.
The invention applies to any cellular network, and in particular, although not exclusively, a GSM network.
To be more precise, the present invention concerns a method of spatial location of a mobile station moving in a cell of a communication network and a corresponding base station with omnidirectional antenna controlling the cell, mobile stations of the communication network and signaling.
2. Description of the Prior Art
A conventional mobile radio network comprises cells in each of which one or more mobile stations move around. Each cell is controlled by a base station. In this context the network can be any mobile radio network, in particular with regard to the shape and the number of cells.
In SDMA systems the cell is divided into a plurality of angular sectors centered on the base station. The base station must therefore be able to determine the angular sector containing a mobile station. In particular this enables the choice of a traffic channel (associated with a particular frequency) to be allocated to the mobile station.
An array of antennas is conventionally used associated with a specific algorithm, for example an ESPRIT type algorithm (Estimation of Signal Parameters via Rotational Invariance Techniques) or a MUSIC type algorithm (MUltiple Slgnal Classification).
The above prior art methods have the drawbacks of being complex, of requiring large volumes of computation and of using a plurality of antennas in each base station.
U.S. Pat. No. 5,508,707 describes a method of determining the geographical position of mobile stations sending an emergency call. The process disclosed comprises the following steps:
determining the contours (in terms of maximum and minimum error estimates) of the coverage areas of the base stations that can receive a call transmitted by a mobile unit to define a first bounding area that describes the relative position of the mobile unit; PA1 determining which lobes (in an SDMA system) or which filters (in a non-SDMA system) of various base stations are in communication with the mobile unit to determine a second bounding area that describes the relative position of the mobile unit; PA1 determining where the first and second bounding areas intersect so as to obtain a relatively precise description of the position of the mobile unit.
Accordingly, the above method necessitates a plurality of base stations.
What is more, the above method, like those described above, has the drawback of using an array of antennas to determine a precise location of the mobile station, which necessitates complex processing and represents a solution that is difficult to implement.
An objective of the invention is to mitigate the various drawbacks of the prior art.
To be more precise, a first objective of the invention is to provides a simple method of spatial location of a mobile station moving around in a cell and means associated with that method making it simple and easy to implement.
A complementary objective of the invention is to provide a method of the above kind that requires only one omnidirectional antenna in each base station.
Another objective of the invention is to provide a method of the above kind which optimizes the allocation of communication resources.